I think most folks would just give him the ball. Souvenir balls are nice but unless it was also your first big league game the ball has more sentimental value for him than anybody else. But the “fan” is almost definitely a ball hawk, just looking to make cash.
This guy sounds like all the non-fans who attened the first couple years of baseball when PacBell Park first opened. They bought out all the tickets, not because they loved the game, but because it was "the place" to be seen. Didn't have much of a clue about the game but hey - they were there.
There is nothing more annoying (to me) than going to watch a baseball game and having the people in your section getting up and down, up and down (beer, food, beer, bathroom, more beer), walking in front of you (excuse me, excuse me)and yapping on their cell phones rather than watching the game.